In order to examine the possible role of metal-bound cysteinates as proton storage and/or transfer sites in biology, a series of late transition-metal thiolate complexes which model the metalloenzymes hydrogenase (Ni), alcohol dehydrogenase (Zn), and nitrile hydratase (Fe), will be synthesized using a template schiff-base reaction. S....H interactions will be probed in protic media and protonated M-(RS)-H+ species isolated where possible. Reactions with substrates H2 (Ni-SR), R-OH (Zn-SR), and H2O (Fe-SR) will be examined and mechanisms involving heterolitic addition of H-H or C-H bonds across a M-SR will be tested. The relationship between structure and reactivity will also be probed in order to assess the features which are responsible for metalloenzyme activity. Mechanisms leading to methane formation from -(CH2)n-S-Me substrate analogues will be examined using methyl coenzyme M reductase model compounds which consist of Ni(I)N4 macrocycles containing covalently attached (tethered) thioether arms. Reactivity (i.e., C-S bond cleavage) -dependence on arm-length (n=2, 3) and R-group (R= Me, Et, CH2Ph) for a series of tethered Ni(N4-(CH2)n-S-R) macrocycles will be examined. In order to test our single electron transfer mechanism the correlation between Ni....SR2 interaction and reactivity will be examined and radical intermediates will be probed for using freeze quench EPR. The kinetics of C-S bond cleavage will be monitored by low T UV/vis and products (CH4, CH3-CH3, CH3Ph) will be detected using 1H NMR and GC/MS.